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The layer of skin you see, the Epidermis, is made up of the cells
that manufacture skin. The outer layer is dead skin cells. Underneath
are flat, scale-like cells called Squamous cells, and beneath them are
round basal cells. The epidermis also contains cells that produce melanin,
which gives skin its color.
Every hair on your body grows from a live follicle with roots in
the fatty layer called subcutaneous tissue. The sebaceous glands
secrete sebum, an oily substance that helps keep skin from drying out.
Most of the glands are located in the base of hair follicles. Acne starts
when the tiny hair follicles become plugged with these oily secretions.
Subcutaneous tissue, mostly made up of fat, lies between the dermis
and muscles or bones, and contains blood vessels that expand or contract
to help keep your body a constant temperature. Fatty tissue is distributed
unevenly over your body and thins with age.
The dermis contains two types of fibers that lessen in supply with
age: Elastin, which gives skin its elasticity, and collagen, which provides
strength. The dermis also contains blood and lymph vessels, hair follicles,
sweat glands and the sebaceous glands, which produce oil.
When your body gets hot or is under stress, these glands produce
sweat, which evaporates to cool you. Sweat glands are located all over
the body, but are especially abundant in your palms, soles, forehead and
underarms. The Apocrine glands are specialized sweat glands that emit
an odor. To help keep your body a constant temperature, blood vessels
in the skin dilate in response to heat or constrict in response to cold.
Only your lips, palms and the soles of your feet are truly hairless. Most
hair helps protect the body in some way: on the scalp, it provides
some insulation and protects you from sun exposure; in eyelashes and eyebrows,
it helps protect your eyes.
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